Passenger vehicles are commonly equipped with restraint systems, typically in the form of seat belts, for restraining primarily an upper part of the vehicle occupant in case of a frontal crash. However, it is known that the vehicle occupant may submarine or slip forward under the seat belt at the time of a vehicle crash. This can occur if the seat belt fails to restrain the pelvic part of the vehicle occupant for various reasons, and severely impairs the capability of the scat belt to restrain the vehicle occupant. Also, it is important to restrain the vehicle occupant at an early time point as possible to ensure the safety of the vehicle occupant at the time of a vehicle crash. Air bags are another form of such restraining systems for restraining an upper part of the vehicle occupant.
Restraint systems for restraining a lower part of the vehicle occupant have been proposed in various forms. Such an example is illustrated in FIG. 8. A laterally extending restraining pipe member 32 is pivotally supported on either lateral end thereof with respect to a seat frame 33 by arm members 34, and a power actuator 35 for vertically upwardly moving the corresponding arm member 34 provided on one of the side walls of the seat frame 33. The restraining pipe member 32 is normally situated under a front part of a seat bottom cushion 31. The power actuator 35 is incorporated with a pyrotechnical actuator for driving the restraining pipe member 32 upward along with the corresponding part of the seat bottom cushion 31. The lower part of the vehicle occupant can be thus engaged by the restraining pipe member 32 which is raised at the time of a crash, and the vehicle occupant is thereby prevented from submarining.
However, according to this previous proposal, owing to the use of a pyrotechnical actuator, once the restraint system is actuated, it is not possible to restore the restraint system back to the original state. Therefore, once the restraint system is actuated, the vehicle seat becomes unfit for any subsequent use although the seat may be otherwise in a prime condition.
In recent years, vehicle occupant restraint systems based on prediction of an occurrence of a vehicle crash have been proposed. In such a system, the restraint system needs to be actuated when a vehicle crash is likely to happen, but it is also possible that the prediction turns out to be wrong. In other words, it is very possible that the restraint system is actuated a number of times without experiencing any actual vehicle crash. Therefore, the restraint system of this kind is desired to be suited for repeated actuation. At the same time, the restraint system is capable of withstanding the load of restraining the vehicle occupant at the time of a vehicle crash.